1. Field of the Invention
The present invention relates generally to extracting viscous materials from containers using a pump assembly that includes a follower plate which is lowered into the container as material is removed. More particularly, the present invention relates to a method and apparatus for extracting excess material from containers after the follower plate has moved into the container to the point where the pump has lost its ability to further remove material.
2. Description of the Related Art
Pumps for pumping viscous fluids from relatively large containers such as cylindrical drums conventionally employ a follower plate, with the pump mounted above an orifice through the follower plate. U.S. Pat. No. 4,792,063 to Moore, which is hereby incorporated by reference, describes such pumps. In such systems, the follower plate is introduced into the container as the liquid is evacuated via pneumatic, hydraulic, or spring-driven means or simply by the vacuum that results from the removal of material. The pumping action creates a partial vacuum as the follower plate is drawn into the container, until the pump loses the ability to withdraw further material from the drum. The descending follower plate scrapes excess material from the sides of the container and forces the liquid into the pump to prime it and keep it primed. Normally considerable excess material is left in the container at the point that no further material can be removed. A bag often is inserted into such containers prior to filling to facilitate removal of this excess material, but this does not provide an efficient way to remove that material.